package com.nowcoder.community.util;

import org.apache.commons.lang3.CharUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

@Component
public class SensitiveFilter {

    private static final Logger logger = LoggerFactory.getLogger(SensitiveFilter.class);

    //替换符
    private static final String REPLACEMENT= "****";

    //根节点
    private TrieNode rootNode = new TrieNode();

    @PostConstruct
    public void init(){
        try (
             InputStream is = this.getClass().getClassLoader().getResourceAsStream("sensitive-words.txt");
             BufferedReader reader =new BufferedReader(new InputStreamReader(is));
             ){
            String keyword;
            while ((keyword = reader.readLine() ) !=null ) {
                // 添加到前缀树
                this.addKeyWord(keyword);
            }
        }catch (IOException e){
            logger.error("加载敏感词文件失败" + e.getMessage());
        }

    }

    //将一个敏感词添加到前缀树里
    private void addKeyWord(String keyword){
        TrieNode tempNode = rootNode;
        for (int i = 0; i < keyword.length(); i++) {
            char c= keyword.charAt(i);
            TrieNode subNode=tempNode.getSubNode(c);

            if(subNode==null){
                //初始化子节点
                subNode = new TrieNode();
                tempNode.addSubNode(c,subNode);
            }

            //指向子节点,进入下一轮循环
            tempNode =subNode;

            //设置结束标识
            if (i == keyword.length()-1){
                tempNode.setKeywordEnd(true);
            }
        }
    };

    /**
     * 过滤敏感词
     * @Param text带过滤文本
     * @return  过滤后文本
     */
    public  String filter(String text){
        if (StringUtils.isBlank(text))  {
            return null;
        }
        //指针一
        TrieNode tempNode = rootNode;
        //指针2
        int begin =0;
        //指针3
        int position =0;
        //结果
        StringBuilder sb = new StringBuilder();

        while (position <text.length()){
            char c=text.charAt(position);

            //跳过符号
          if (isSymbol(c)) {
              //若指针1位于根节点,将此符号计入结果,指针2往下走一步
              if (tempNode == rootNode) {
                  sb.append(c);
                  begin++;
              }
              //无论符号在开头或者中间,往后走一步
              position++;
              continue;
          }

          //检查下级节点
           tempNode = tempNode.getSubNode(c);
          if (tempNode == null){
              //以begin开头字符不是敏感词
              sb.append(text.charAt(begin));
              //进入下一个位置
              position=++begin;
              //重新指向根节点
              tempNode = rootNode;
          } else if (tempNode.isKeywordEnd()){
              //发现敏感词,将bengin-position替换掉
              sb.append(REPLACEMENT);
              //进入下一个位置
              begin = ++position;
              //重新指向根节点
              tempNode = rootNode;
          } else {
            //检查下一个字符
              position++;
          }
        }
        // position遍历越界仍未匹配到敏感词
        //将最后一次字符计入结果
        sb.append(text.substring(begin));
        return sb.toString();
    }

    //判断是否为符号
    private boolean isSymbol(Character c){
        // 0x2E80~0x9FFF 是东亚文字范围
        return !CharUtils.isAsciiAlphanumeric(c) &&(c < 0x2E80 || c > 0x9FFF);
    }
    //前缀树
    private class TrieNode{

        //关键词结束标识
        private boolean isKeywordEnd = false;

        // 子节点,key为下节点,value为下节点
        private Map<Character,TrieNode> subNodes = new HashMap<>();

        public boolean isKeywordEnd() {
            return isKeywordEnd;
        }

        public void setKeywordEnd(boolean keywordEnd) {
            isKeywordEnd = keywordEnd;
        }

        // 添加子节点
        public void addSubNode(Character c, TrieNode node) {
            subNodes.put(c, node);
        }

        // 获取子节点
        public TrieNode getSubNode(Character c) {
            return subNodes.get(c);
        }
    }
}
